Credit: Jamie Squire/Getty Images

Former NFL running back Larry Johnson says he believes he has chronic traumatic encephalopathy, a brain disease that doctors say can be caused by repeated blows to the head.

CTE can be only diagnosed after someone dies.

Johnson, who last played in the NFL in 2011, says he has mood swings, headaches and forgets a lot of things, which he calls "Blank spots." He also says he is prone to violence and self-destructive impulses.

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